1. Field of the Invention
The present invention relates generally to artificial firelogs containing additives that create a crackling sound accurately mimicking the sounds produced during the burning of natural wood logs.
2. Description of the Prior Art
Artificial or synthetic fireplace logs are manufactured from a broad range of flammable cellulosic components in combination with a binder, and possibly other additives. Typical flammable cellulosic components include wood particles, pulp, shavings or chips, sawdust, ground bark, shredded paper or cardboard, waxed cardboard, charcoal powder, spagnum moss, and agricultural waste materials such as straw, bagasse, grass clippings, leaves, cotton linter, rice hulls, peanut or other nut shells and coffee grounds. The binder is typically a flammable wax such as paraffin wax or slack wax or flammable vegetable oils such as stearic and/or paimitic acid or other fatty acids or esters. However, numerous other combustible components are used or could be used and the foregoing lists of materials are not intended to limit the composition of flammable artificial firelogs for purposes of the present invention. Further, as is well known, artificial firelogs may also contain additives including chemicals designed to color or otherwise modify or retard the flame, add aroma or change the burning characteristics to more closely mimic the burning of natural logs.
A single artificial log, which may weigh 5-6 pounds, is designed to burn unattended for about 3-4 hours. For comparison, a 5-6 pound natural oak log will burn for about ⅓ of that time. To get a comparable burning time, 3 natural firelogs of 5-6 pounds are generally burned at one time. Also, to sustain a 3-4 hour burn with the desired ambience and flame intensity, it is often necessary to stir the natural log fire and turn over the logs for a relatively uniform and intense burn.
Natural burning logs generate an audible snapping, popping and crackling sound as the moisture and oils naturally occurring in the wood are heated, creating steam and vapor. This expanding steam and vapor causes the wood to crack creating the sounds. However, these sounds do not persist throughout the burning cycle. As the wood is heated by the surrounding flames, the vaporizable components are dissipated long before the natural log stops burning. As a result, the sounds start as the natural wood starts to burn, increases in a random, but persistent manner for a period of time followed by a tapering off of the frequency of the sound. This is illustrated in FIG. 1, a graphical representation of the intensity of the sounds produced as a function of time during the first 1xc2xd hours of burning of a 6.6 pound natural pine cordwood log. The longevity, persistence and frequency of the sounds produced by burning a natural firelog depends on the moisture and oil content of the natural wood and the density and hardness of the wood. However, for typical natural firewood, the sounds persist for about one-half of the burning cycle.
In the absence of crackling additives, artificial firelogs burn much more quietly than natural logs. Accordingly, artificial firelogs that contain crackling additives have been developed in an effort to simulate the sound intensities and patterns produced during the burning of a natural log. For example, U.S. Pat. No. 5,118,539 to Sebby, et al., discloses artificial firelogs containing crackling additives in the form of seeds found in bird food mix, particularly hemp, millet and sunflower seeds, to provide a popping sound. U.S. Pat. No. 5,868,804 to Williams, et al., is directed to an artificial log having a crackling additive consisting of 1) mustard, flax, cumin, or sesame seed, or a combination thereof, 2) synthetic hollow spheres or microspheres, or 3) a combination of seed component and microspheres, to provide an audible crackling sound during burning of the logs.
These prior art compositions either have a very short lived popping sound or the sound persists for a significantly longer portion of the burning cycle, thus creating an unrealistic simulation of the burning of natural logs, or the sound is not of a quality or volume to simulate burning of natural logs. Often, there is little randomness or change in sound intensity during the burn. Accordingly, there has been a need for a synthetic log that more closely simulates the actual performance of burning natural logs.
U.S. Pat. No. 6,017,373, issued Jan. 25, 2000, to Frisch and incorporated herein by reference in its entirety, discloses artificial firelogs comprising one or more flammable materials, preferably cellulosic materials, and a wax binder blended and shaped in the manner typical of the artificial logs available in the past. Coriander seed is added to this composition during fabrication of the artificial log. The seed produces a random popping sound, with a volume similar to burning natural wood logs, for about 50% of the burning cycle of the log. The seed may be supplemented by replacing up to about one third of the seed with an equal percentage of naturally occurring geological materials of volcanic origin if a consistent popping sound is desired throughout the remainder of burning cycle of the artificial log. The objective of adding these materials is to generate sound more typical of burning natural logs.
Artificial firelogs in accordance with Frisch provide a substantial improvement in the simulation of the actual performance of burning natural firelogs but nevertheless there continues to be a need for artificial firelogs that even more closely simulate the performance of natural logs. In addition, the production of natural crackling additives such as coriander seed is seasonal and typically requires specialized conditions such as temperate growing zones.
In accordance with the broad principles of the present invention, there is provided an artificial firelog comprising combustible materials, a combustible binder and an effective amount of a sound generating additive to provide a crackling sound during at least a portion of the burning of the firelog wherein the crackling additive comprises particles of coke. Although a variety of xe2x80x9chard cokesxe2x80x9d such as petroleum coke will provide the desired sound, the preferred coke for use in the artificial firelogs of the present invention comprises metallurgical or xe2x80x9cmetxe2x80x9d coke.
In accordance with another aspect of the invention, the size of the particles of coke is preferably below about 4 mm.
The addition range of the particles of coke is preferably between about 1% and about 35% by weight of the firelog on a dry basis.
Pursuant to yet another aspect of the present invention, the particles of coke are provided with a moisture content between about 2% and about 20% by weight. Such moisture levels helps produce louder crackling sounds.
Pursuant to yet another specific embodiment of the artificial firelog of the present invention, besides particulate coke, the sound generating additive may also include sound generating natural seed such as coriander seed. More particularly, where the supplemental natural crackling additive is coriander seed, the ratio of coriander seed to particulate coke is preferably between about 1:1 to about 1:3, by weight.